Fleetwood Mac's song inspired by Mary Bartlet Leader's novel Triad was “Rhiannon.”
Stevie Nicks discovered the name while reading Triad: A Novel of the Supernatural, published in 1973. The novel mentions the Welsh figure Rhiannon, although its characters differ substantially from the figures of Welsh mythology. Nicks was captivated by the name and began writing a song around the mysterious character.
Nicks composed the song on piano and made an early cassette demo before recording it with Fleetwood Mac. The track appeared on the band's 1975 self-titled album, recorded soon after Nicks and Lindsey Buckingham joined the group. It became one of Nicks's defining compositions and a major part of Fleetwood Mac's live identity.
A common mix-up is to assume the song was directly adapted from medieval Welsh mythology. Nicks later recognized parallels between her imagined “Rhiannon” and the Welsh legendary figure, but the immediate inspiration was Leader's novel. The single reached No. 11 on the U.S. Billboard Hot 100 in 1976.